Crystalline salt forms of Boc-D-Arg-DMT-Lys-(Boc)-Phe-NH

1. A method of making Compound (II), the method comprising

deprotecting compound (I),

 or a salt thereof, thereby making compound (II)

 or a salt thereof;

wherein the step of deprotecting comprises:

a. preparing a mixture of a crystalline form of Compound (I), triisopropylsilane, and 2,2,2-trifluoroethanol; and

b. adding concentrated hydrochloric acid to the mixture;

wherein the crystalline form of Compound (I) is a crystalline form of a salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta as described in any one of Tables A′-F′:

wherein Table A′ is:

Pos. [°2θ]

3.7579

4.2659

6.5526

7.2841

8.0800

8.5065

9.7875

10.6288

12.0543

12.7809

13.3068

14.1827

14.5619

15.0219

16.1288

16.9425

18.0211

18.7982

19.1243

19.6849

20.1376

20.5047

20.9553

22.0163

22.6867

23.2292

24.0145

24.5746

25.1662

25.9049

26.4986

27.4092

27.9577

29.2173

30.4972

30.9418

31.7727

32.2938

33.4213;

Table B′ is:

Pos. [°2θ]

3.7036

4.4432

6.5634

7.4018

9.7210

10.6210

11.0920

12.7331

13.1598

14.0930

14.7901

16.7103

17.1509

18.0233

18.5346

18.7979

19.1239

19.5235

19.8085

20.1544

20.6070

20.8573

21.3109

22.0189

22.6758

23.0757

23.6744

23.9728

24.4777

25.7316

26.4407

27.7972

30.1162

32.1646;

Table C′ is:

Pos. [°2θ]

5.1621

8.9359

10.7664

13.3445

14.3884

15.9863

17.2952

18.8443

19.5521

21.0051

23.2998

24.6506;

Table D′ is:

Pos. [°2 Th.]

5.4291

8.0335

9.0773

10.8149

13.4288

14.7938

15.7960

17.5693

18.9795

19.6937

21.3056

22.2563

24.1299

25.7352

27.6495

30.9496;

Table E′ is:

Pos. [°2θ]

4.0824

7.2188

7.7660

8.1685

8.7856

10.1057

11.7275

12.0519

12.2864

12.7774

13.2740

13.6796

14.4861

14.9214

15.1377

15.5347

16.1829

17.7646

18.1548

18.5392

18.9751

19.9095

20.3639

21.0328

21.9414

21.9676

22.2732

22.8116

23.3197

23.5325

24.0190

24.8019

25.2913

25.6339

26.6566

27.7426

28.2705

28.9314

29.2563

30.0846

30.7947

31.5899

31.9371

32.8553;

Table F′ is:

Pos. [°2θ]

3.6742

4.4204

6.7177

7.0320

8.2133

9.8583

10.2604

12.3942

13.2923

13.6972

14.1013

14.6960

15.7923

16.4926

17.0775

17.2537

18.0813

18.4075

18.9537

19.5451

19.7885

20.2166

20.6718

20.8819

21.6381

22.2851

22.6611

23.0749

24.3020

24.7773

25.5656

26.6658

27.2542

27.7067

28.3209

29.3217

30.1348

30.4172

31.1772

32.4960

33.6018.

2. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of a hydrochloride salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.8, 4.3, 9.8, 14.6, 18.0, 18.8, 20.9, and 22.7.

3. The method of claim 2 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.8, 4.3, 6.5, 7.3, 9.8, 13.3, 14.2, 14.6, 16.1, 16.9, 18.0, 18.8, 19.1, 19.7, 20.1, 20.5, 20.9, 22.0, 22.7, 23.2, 24.0, 25.2, and 25.9.

4. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of a hydrochloride salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of 3.7, 4.4, 6.6, 9.7, 14.8, 18.0, 18.5, 18.8, 19.1, 20.9, and 22.7.

5. The method of claim 4 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 6.6, 7.4, 9.7, 10.6, 13.2, 14.1, 14.8, 16.7, 18.0, 18.5, 18.8, 19.1, 19.5, 19.8, 20.1, 20.6, 20.9, 21.3, 22.0, 22.7, 23.1, and 24.0.

6. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of a tosylate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.2, 8.9, 14.4, 17.3, 18.8, 19.5, and 21.0.

7. The method of claim 6 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.2, 8.9, 10.8, 13.4, 14.4, 16.0, 17.3, 18.8, 19.5, 21.0, 23.3, and 24.6.

8. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of a mesylate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.4, 13.4, 14.8, 15.8, 17.6, 19.0, and 21.3.

9. The method of claim 8 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.4, 10.8, 13.4, 14.8, 15.8, 17.6, 19.0, 19.7, 21.3, 22.3, 24.1, and 25.7.

10. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of an oxalate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 7.8, 10.1, 12.8, 17.8, 18.5, 19.9, and 22.3.

11. The method of claim 10 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 4.1, 7.2, 7.8, 8.1, 10.1, 12.0, 12.8, 13.3, 14.5, 14.9, 17.8, 18.1, 18.5, 19.9, 20.4, 21.9, 22.0, 22.3, and 23.5.

12. The method of claim 1 , wherein the crystalline form of Compound (I) is a crystalline form of a benzoate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 14.1, 18.1, 18.9, 20.7, 22.3, and 24.3.

13. The method of claim 12 , wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 6.7, 9.9, 13.3, 13.7, 14.1, 15.8, 17.2, 18.1, 18.4, 18.9, 19.5, 20.7, 20.9, 21.6, 22.3, and 24.3.

14. The method of claim 1 , wherein the mixture is a slurry.